This invention relates to a sealant for prefabricated insulating glass windows and doors.
Prefabricated insulating glass windows and doors generally comprise a rectangular sash with a rabbet adapted to receive the edges of an insulating glass unit and stops nailed to the sash to keep the insulating glass in place. Preferably the insulating glass is automatically bedded and glazed in place with a sealant between the sash rabbet and the edge faces of the bottom sheet of glass of the insulating glass unit and with a sealant between the edge faces of the top sheet of glass of the insulating glass unit and the stops.
The sealant between the edge faces of the top glass sheet and the stop usually comprises a silicone rubber. The sealant between the edge faces of the bottom glass sheet has been a similar silicone rubber or a foam strip.
When a silicone rubber or similar sealant is used for the seal between the edge face of the bottom sheet of glass and the sash rabbet, and the sealant layer is too thin, there is a tendency for the seal to be broken and for the bottom sheet of glass to crack at points of stress concentration which develop when the glass sheets work in response to changes in atmospheric pressure and temperature.
The sealant layer can become too thin when the insulating glass unit is set on the sash rabbet and the weight of the unit squeezes out the sealant.
In an effort to avoid this problem, some manufacturers use strips of foam as the sealant between the sash rabbet and the edge faces of the bottom sheet of glass. While the strips of foam avoid the cracking problem as the glass sheets work, they have another problem, which is that the strips tend to shrink longitudinally and leak cold air at the corners and develop pockets of moisture. Additionally, the foam strips have to be applied by hand. Silicone rubber sealant can be applied automatically.
There generally is not a stress concentration problem at the seal between the edge faces of the top sheet of glass and the stops because the stops are nailed in place and give or work enough to avoid stress concentration points. Also, there is less tendency for the layer of silicone rubber sealant to become too thin because when the stops are applied, they do not squeeze out the sealant. Even with sash units which are made of extruded aluminum sections or the like, the stops for the top sheet of glass are more forgiving and there is less tendency for areas of stress concentration to develop.
The problem, therefore, is with the seal between the edge faces of the bottom sheet of glass of the insulating glass unit and the rabbet of the sash.